1. Field of the Invention
The present invention relates to a monolithically integrated resistive structure with power IGBT (Insulated Gate Bipolar Transistor) devices.
More specifically, the invention relates to a device being integrated on a semiconductor substrate of a first type of conductivity crowned by a semiconductor layer of a second type of conductivity comprising a voltage controlled resistive structure and an IGBT device and a method of manufacture thereof.
2. Description of the Related Art
As it is known, high voltage resistors integrated on a semiconductor material substrate or chip are widely used in the field of monolithically integrated power devices, for example, of devices manufactured with VIPower technology, according to which power devices are integrated in a first region of the chip, called the power region, whereas the relevant control devices are integrated in a second region of the same chip, called the control region, being distinct and electrically insulated from the power region.
Moreover, in other applications, it is also necessary to provide, inside the control region, a biasing voltage derived from a biasing voltage of the substrate by means of a divider realized by using a resistor connected between the substrate and the control region. However, in order for this resistor to be able to withstand the high values the substrate biasing voltage can reach, as it is known (up to 2 kV), it needs to have fairly high resistance values, which generally is 100 kΩ or higher so as to limit the power dissipation given by P=R*l2, P being the dissipated power value, R the resistance value of the resistor and l the current flowing in the resistor.
A prior art solution for manufacturing a resistor having the above cited resistance values provides the integration in a semiconductor substrate of a high resistant doped region having an opposite conductivity with respect to that of the substrate itself.
Although advantageous in several aspects, this solution has various drawbacks when a resistive structure has to be integrated in a semiconductor substrate made for integrating devices of the IGBT type as it is shown in FIG. 1.
In particular, in the case of IGBT applications, on a semiconductor substrate 1, which comprises a first region 2 of the P+type and a second region 3 of the N type, a highly resistant doped region 4 is integrated having an opposite conductivity with respect to that of the second region 3 of the N type whereon it is integrated. This doped region 4 has a planar configuration and possibly it can also be serpentine-like and it comprises a high voltage resistor 5.
The final device 14 thus comprises an insulating layer 6, deposited on the second region 3, whereon openings 7 are formed for performing the electrical connection with a metal layer 8 formed on the insulating layer 6. The final device 14 is thus completed by forming a substrate electrode 9 on the back of the semiconductor substrate 1.
As it is shown in the figure, the presence of the high voltage resistor 5 forms a PNP parasite transistor 10 whereon emitter and collector terminals 11 and 12 are respectively connected to the first region 2 and the doped region 4, whereas the base terminal 13 is connected to the second region 3.
Accordingly, there remains a need in the art to provide a monolithically integrated high voltage resistive structure with IGBT devices, having such structural and functional characteristics so as to avoid the growth of parasite transistors and to overcome the limits and drawbacks that still affect the devices realised according to the prior art.